Megapixel and How to Understand Them

[cjstarr]

Just when do you have enought megapixels? Is 10mp good and if it is does this mean that 20mp will be that much better? I have read that some dslr's have as high as 46mp's and there is a cmos that has been developed that will go to 120mp's. Of course it sells for $44,000 from what I read.
So just how good of a picture will you get from a 10mp, 16pm, or 20mp?
Are you going to see that much of a diferents between them?

 

[wbeem]

Megapixels have nothing to do with quality of your image. It's about the size of your image. I have a D700 with 12 MP and a D800 with 36 MP. The D800 has somewhat better image quality, but that's not because of the megapixels.

How many megapixels do you need? That depends upon your output. If you're just posting online, you can do fine with a very low amount, like my old D70. If you're printing a billboard, you want more megapixels. My D700 has good print quality up to 36" x 24", and perhaps a little more.

 

[DSLRuser]

^^ What he said ^^

in general, the # of megapixals is really a stat you should not look at. As long as you are comparing cameras from the same model year it should not matter.

I say this because 5 years ago, entry level cameras had around 5 mega pixals sensors, and higher end tended to be around 12.

now that has shifted to 12 for entry level and around 20 for higher end. (excluding pro)

point being, if you look at a mid lebel cannon and a mid level nikon, the sensors will be close in mega pixals. there are many many other features that determine what camera to buy.

where this gets confusing is if you look at older equipment versus newer. A mid level nikon d5000 from 5 years ago had considerably less MP than a new d5200.

I could go on and on and just confuse you more. Bottom line, MP willindirectly determine how large a picture you can print. but even that are guideines based on your final output desired.

 

[cjstarr]

I thought megapixals filled in the space in a picture? Lets say you have a 4 X 6 picture taken with a 10 megapixal camera will not the number of dots it takes to fill in the picture be larger and have less as many then one that was taken with a 20 megapixal camera? After all the 20 megapixal camera has twice as many. Now blow the picture up to an 8 X 10 doesn't this spread the pixals out. Don't you have a set amount of pixals in each only now you have a larger space to fill making the 4 X 6 image sharper and clearer, right or wrong then the 8 X 10.
In my mine it's like pixals per square inch, the more you have the better and sharper the image.

 

[ukstitch]

In my mine it's like pixals per square inch, the more you have the better and sharper the image.

This is true, but printers can only print so many dots of ink per square inch. So if you have more megapixels (dots) than the printer can print then the printer will work out the best colour to use e.g. if you have 4x more pixels than you can print then the printer will treat each 2x2 set of pixels as a single pixel.

But - if you enlarge the print to be much larger, then the picture that had more megapixels than was needed will now have the correct number and look just as sharp as before because the dots per inch is the same as before.

The picture that had exactly the right number of pixels on the other hand will now start to look less sharp as the number of dots per inch decreases and the size of each dot increases as a result.

The other use that's not been mentioned here for megapixels is cropping - if you have lots of megapixels, you can crop your picture and still be able to get a good sized print from the cropped picture.

 

[hakepb]

I thought megapixals filled in the space in a picture? Lets say you have a 4 X 6 picture taken with a 10 megapixal camera will not the number of dots it takes to fill in the picture be larger and have less as many then one that was taken with a 20 megapixal camera? After all the 20 megapixal camera has twice as many. Now blow the picture up to an 8 X 10 doesn't this spread the pixals out. Don't you have a set amount of pixals in each only now you have a larger space to fill making the 4 X 6 image sharper and clearer, right or wrong then the 8 X 10.
In my mine it's like pixals per square inch, the more you have the better and sharper the image.

Which camera looks like it would "fill in" a picture better?
Here's a screenshot from DPReviews studio comparison tool. These show crops (just a little part of the entire image) from their in-studio comparison scene:

The camera on the left (top and bottom) has 10MP. The camera on the upper right has 12MP, and the camera on the bottom right has 16MP.

I would much prefer a print from the 10MP camera.
Now, this is a scientifically flawed comparison, because its DSLr vs PnS so you see more of sensor size and lens quality comparison.
More MP has a disadvantage, the smaller pixels may have a harder time getting enough light in dark conditions. And even in the best conditions, more MP can get to the point of showing flaws in some lenses. More MP can make cameras and computers slower processing each picture.

 

[photo_chick]

I thought megapixals filled in the space in a picture? Lets say you have a 4 X 6 picture taken with a 10 megapixal camera will not the number of dots it takes to fill in the picture be larger and have less as many then one that was taken with a 20 megapixal camera? After all the 20 megapixal camera has twice as many. Now blow the picture up to an 8 X 10 doesn't this spread the pixals out. Don't you have a set amount of pixals in each only now you have a larger space to fill making the 4 X 6 image sharper and clearer, right or wrong then the 8 X 10.
In my mine it's like pixals per square inch, the more you have the better and sharper the image.

That is the basic idea, but it doesn't always translate to paper that way. On the screen more pixels means a larger image to view. In print it's different and it helps me to remember the formula PIXELS X DPI = INCHES so I know the minimum I need to get a print. If your image file has a ton more pixels than you need to print pixels will be eliminated either by you or by the software. Most people don't realize that step happens when you make a print.

There's pro's and cons to more pixels as well. the main con is that more pixels on the sensor can also mean more noise because they're smaller and closer together. But higher resolution can also give you the ability to crop in on an image without significant loss of details. It can mean more fine detail from having a larger file to start with as well. You just have to weigh it all and see which things are more important for you. People who say you don't need more megapixels aren't looking at everything though. There are situations where you do need them and there are situations where you don't want them. Like everything in photography what you need comes down to your personal needs.

The images hakepb posted are a pointless comparison because there are other factors than just pixel resolution there. The resolving power of the lens also comes into play (among other things). And that's another point. These super high MP cameras are starting to out pace the resolving power of existing lenses. It's not just about flaws in the lenses but the overall ability of the lens to clearly render details. So if you buy a super high MP camera to get finer details be prepared to pony up the cash for the high end lenses to support it, otherwise you've wasted money on the camera because you won't see those gains.

 

[havoc315]

Resolution reaches a point where monitors, printers, and the human eye can't see the difference. Thus, for your typical photograph sizes, you simply don't need more than 8-10mp.

That said-- having more megapixels does have an advantage in being able to crop a picture more heavily. Crop out half of a 8 mp photograph, and what's left will be low resolution. Crop out half of a 20mp photograph and have plenty left for a high resolution photo.

 

[cjstarr]

havoc315,so am I to understand that a camera with a high megapixal should be able to use a wide angle lens to take the shot with, then croped and blowed up and still have a great looking picture.

 

[havoc315]

havoc315,so am I to understand that a camera with a high megapixal should be able to use a wide angle lens to take the shot with, then croped and blowed up and still have a great looking picture.

Whether wide angle or telephoto... More megapixels will give you more freedom to crop. If you typically only clean up the edges in a picture, not a big difference. But if you entirely re-compose a shot with cropping, more mp gives more flexibility.

 

[wbeem]

havoc315,so am I to understand that a camera with a high megapixal should be able to use a wide angle lens to take the shot with, then croped and blowed up and still have a great looking picture.

That's one use. I know some folks who own the D800 who are now shooting much wider than they would with a D700. The reason is so they can go back to crop differently in post. If you don't have the subject when you capture it, you can't add it later (without composition). However, you can always eliminate by changing your crop later.

That doesn't mean you want to use a wide angle lens, though. Lens selection causes other issues, including compression. The lens doesn't just give you an angle of view. It also affects how the subjects in the photo relate to each other, including their apparent size in the final image. There are times when it's much wiser stand farther back and use a telephoto than get closer and use a wide angle.

 

[photo_chick]

Resolution reaches a point where monitors, printers, and the human eye can't see the difference. Thus, for your typical photograph sizes, you simply don't need more than 8-10mp.

That said-- having more megapixels does have an advantage in being able to crop a picture more heavily. Crop out half of a 8 mp photograph, and what's left will be low resolution. Crop out half of a 20mp photograph and have plenty left for a high resolution photo.

Not entirely true. File resolution is about more than just cropping. And with lenses that can resolve the image equally to the resolution of your sensor more megapixels can make a noticeable difference in some situations. My 15MP DSLR has a noticeable difference in how it renders details over my 8MP DSLR when lens and print size are equal.

Again though, more isn't better for all situations because there are other factors involved.

havoc315,so am I to understand that a camera with a high megapixal should be able to use a wide angle lens to take the shot with, then croped and blowed up and still have a great looking picture.

It's not as simple as cropping in. While you will crop and still have a technically high resolution file you're going to loose some image quality. Not a lot if you're just cropping a little, but it is there. It's digital zooming instead of optical zooming. It's not just about pixels. The projected image from the lens is still the same size on the sensor. So yes, while you can crop in and it's a nice option to use I wouldn't want to rely on it to zoom in. Look at it this way, if you had a point and shoot would you want digital or optical zoom? And then there's compression and perspective as well as depth of field that comes in to play like wbeem touched on.

 

[boBQuincy]

Resolution reaches a point where monitors, printers, and the human eye can't see the difference. Thus, for your typical photograph sizes, you simply don't need more than 8-10mp.

While this is true we have not yet reached the point where we can't see the difference. In fact we are probably not even close yet.

http://www.luminous-landscape.com/u...ters__it_is_all_about_the_small_details.shtml

For typical print sizes we may not *need* more than 3 MP but more does make a difference, a visible difference.

More pixels does not equal more noise, in fact it is the opposite.

http://www.dxomark.com/index.php/Publications/DxOMark-Insights/More-pixels-offset-noise!

If we can afford more pixels it is difficult to lose by going for them as long as we have the $$$, the expertise to utilize the pixels, can carry the extra weight, and are willing to take the time to set up the photograph.

 

[havoc315]

While this is true we have not yet reached the point where we can't see the difference. In fact we are probably not even close yet.

http://www.luminous-landscape.com/u...ters__it_is_all_about_the_small_details.shtml

For typical print sizes we may not *need* more than 3 MP but more does make a difference, a visible difference.

More pixels does not equal more noise, in fact it is the opposite.

http://www.dxomark.com/index.php/Publications/DxOMark-Insights/More-pixels-offset-noise!

If we can afford more pixels it is difficult to lose by going for them as long as we have the $$$, the expertise to utilize the pixels, can carry the extra weight, and are willing to take the time to set up the photograph.

I've always learned that more megapixels, on the same size sensor, contributes to more noise. So I'm curious about what you're saying, the link didn't work.

The first article talked about medium format pixels being of a higher quality, not more megapixels being better.

 

[boBQuincy]

I've always learned that more megapixels, on the same size sensor, contributes to more noise. So I'm curious about what you're saying, the link didn't work.

The first article talked about medium format pixels being of a higher quality, not more megapixels being better.

The Disboards link for some reason does not wish to include the exclamation mark, which is part of the article title.

Read the article on medium format again, it includes some text about merging and averaging pixels which is an option when we have more.

 

[hakepb]

That ! Article is from 2008 and basically states that a "newer" 20mp full frame DSLr has about the same signal to noise ratio as a previous 8MP model...and I think everyone is fine with 20MP on a full frame sensor.

Now, DXO's best low-ISO rated camera is the 12MP Nikon D3s (their Sports rating is the highest ISO with a <30db SNR)

But the D800 and D600 are only about ISO 300 back.

Smaller pixels are still a problem.
The 20MP Full Frame RX1 has a Low Light ISO of 2534.
The APSc 24 MP NEX7 has a low light ISO of 1016
The 20mp 1" RX-100 has a low light ISO of 390.

Within our current camera market, no manufacturer will make an enthusiast camera with lower High ISO performance than a previous model. So, sensor technology improvements facilitate the higher MP counts. Plus, sensors are not all pixels, there is space between the pixels, sometimes used for wires, etc. Sometimes, manufactures figure out how to reduce the "dead space" which allows for 10% more of the same sized pixels...a bit like a screen door made with thinner wire.

 

[Pixel Dust]

More pixels does not equal more noise, in fact it is the opposite.

http://www.dxomark.com/index.php/Publications/DxOMark-Insights/More-pixels-offset-noise!

The article is making a very different assumption that what is being discussed here. It assumes that the pixel sizes for two cameras are the same, but the sensor area increases. Said another way, it's comparing an APS camera with a 35mm lens and a full frame camera with a 50mm lens and higher MP count, so that they have the same field of view. But the pixel sizes are the same. Basically, you are just adding pixels and making the sensor larger. Not cramming smaller pixels into the same area. If you print each camera to the same size, then yes, there will be less noise.

Most people here assume that if the sensor area is the same, when you increase the MP count, the pixel sizes have to be smaller. Therefore, more noise than the smaller MP camera. Even the article itself says, more pixels result in more noise.
"If you keep the same optics, the same sensor size (and therefore the same field of view), what will be the result? Basically, the same amount of light captured by the optics will be shared by more pixels, and since each individual pixel will receive less light, the signal-to-noise ratio (SNR) will be lower. In short, you will end up taking photos with more noise."